JAVA EE: How to find the student whose score is greater than 80 using stream and without using stream

Wednesday, 20 September 2017

How to find the student whose score is greater than 80 using stream and without using stream

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https://www.youtube.com/watch?v=fAAT--78-MI&list=UUhwKlOVR041tngjerWxVccw

Student.java

public class Student implements Comparable<Student> 
{
    private String name;
    private int score;

    public Student(String name, int score)
    {
        this.name = name;
        this.score = score;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public String getName()
    {
        return this.name;
    }

    public void setScore(int score)
    {
        this.score = score;
    }

    public int getScore()
    {
        return this.score;
    }

    @Override
    public String toString()
    {
        return this.name + " - " + this.score;
    }

    @Override
    public int compareTo(Student another)
    {
        return another.getScore() - this.score;
    }
}

NonStreamDemo.java

import java.util.ArrayList;
import java.util.List;

public class NonStreamDemo
{
    public static void main(String[] args)
    {
        List<Student> studentList = new ArrayList<>();

        studentList.add(new Student("Alice", 82));
        studentList.add(new Student("Bob", 90));
        studentList.add(new Student("Carol", 67));
        studentList.add(new Student("David", 80));
        studentList.add(new Student("Eric", 55));
        studentList.add(new Student("Frank", 49));
        studentList.add(new Student("Gary", 88));
        studentList.add(new Student("Henry", 98));
        studentList.add(new Student("Ivan", 66));
        studentList.add(new Student("John", 52));

        /*
         * Find students whose score >= 80
         */
        List<Student> goodStudentList = new ArrayList<>();
        for (Student student : studentList)
        {
            if (student.getScore() >= 80)
            {
                goodStudentList.add(student);
            }
        }

        for (Student student : goodStudentList)
        {
            System.out.println(student);
        }

        /*
         * Calculate average score of all students
         */
        double sum = 0.0;
        for (Student student : studentList)
        {
            sum += student.getScore();
        }

        double average = sum / studentList.size();

        System.out.println("Average score: " + average);

    }

}

Output

Alice - 82
Bob - 90
David - 80
Gary - 88
Henry - 98
Average score: 72.7

StreamDemo.java

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class StreamDemo
{
    public static void main(String[] args)
    {
        List<Student> studentList = new ArrayList<>();

        studentList.add(new Student("Alice", 82));
        studentList.add(new Student("Bob", 90));
        studentList.add(new Student("Carol", 67));
        studentList.add(new Student("David", 80));
        studentList.add(new Student("Eric", 55));
        studentList.add(new Student("Frank", 49));
        studentList.add(new Student("Gary", 88));
        studentList.add(new Student("Henry", 98));
        studentList.add(new Student("Ivan", 66));
        studentList.add(new Student("John", 52));

        /*
         * Find students whose score >= 80
         */
        List<Student> goodStudentList = studentList.stream()
                .filter(s -> s.getScore() >= 80)
                .collect(Collectors.toList());

        goodStudentList.stream().forEach(System.out::println);

        System.out.println("-------------------------------");

        /*
         * Calculate average score of all students
         */
        double average = studentList.stream()
                .mapToInt(s -> s.getScore()).average().getAsDouble();

        System.out.println("Average score: " + average);

        System.out.println("-------------------------------");
        /*
         * Find top 3 students.
         * 
         * As you can see, the operations on a stream can be chained
         * together (intermediate operations) and end with a terminal
         * operation. Such a chain of stream operations is called
         * stream pipeline.
         */
        List<Student> top3Students = studentList.stream()
                .filter(s -> s.getScore() >= 80).sorted().limit(3)
                .collect(Collectors.toList());

        System.out.println("Top 3 Students by Score:");
        top3Students.forEach(s -> System.out.println(s));

    }

}

Output

Alice - 82
Bob - 90
David - 80
Gary - 88
Henry - 98
-------------------------------
Average score: 72.7
-------------------------------
Top 3 Students by Score:
Henry - 98
Bob - 90
Gary - 88